1. Field of the Invention
The present invention generally relates to a twist grip for a twist-grip shifter for bicycles.
2. Background Information
A twist-grip shifter can typically be located on the handlebar of a bicycle, adjacent a fixed hand grip. The type of twist-grip shifter to which the present invention relates can be utilized by the rider to change gears of the transmission of the bicycle, in order to adjust for varying riding surface conditions, such as the grade and evenness of the riding surface. The twist-grip shifter can be disposed adjacent the part of the handlebar which the rider typically grips, such as a hand grip, so that the rider can, by movement of the index finger and thumb, shift the gears of the bicycle transmission without a major movement of the hand and/or arm, which movement could result in loss of control of the bicycle.
A known twist-grip shifter which has a surface structure is disclosed in European Patent No. 0 671 315 A2, where a surface is disclosed which has five rows of knobs or buttons which run axially, which are located in strips along the surface lines, and form strip-shaped areas between these rows of knobs which are not occupied by knobs. This five-axis structure is said to be ergonomically the most favorable shape for this diameter, since such a shape is required by the configuration of the finger joints.
However, ergonomic analyses have shown that when a twist grip is rotated, it is primarily the first two joints of the index finger, which is the finger involved here and is curved around the twist grip, which are decisive in the generation and application of the torque. But the bends of these two joints of the fingers are at a distance from another which corresponds to six to eight strip-shaped elevations over the periphery of a twist grip of the twist grip shifter. The driving of the twist grip then becomes significantly more efficient if the surface has ribs which are engaged in both bends of the index finger. Such ribs are elevations which run axially along the surface lines of the grip part, with a peak which runs in precisely this direction, and which fit best into the joints of the index finger at approximately 90 degrees.
The joints of the fingers are placed in the remaining spaces or depressions, which are defined laterally by sets of ribs which consist of at least one intermediate rib each. Extensions of the ribs and intermediate ribs run in the axial direction through a transitional region toward a larger diameter, where they are not as important ergonomically, but improve traction, which means that the same torque can be applied with less expenditure of effort. Since the twisting force applied by the rider's hand to the twist-grip shifter must be transmitted to the inner components of the twist-grip shifter in order to shift the gears of the bicycle transmission, a rigid, non-rotational connection between the part of the twist grip shifter which the rider rotates when a gear change is desired and the inner components of the twist-grip shifter is highly desirable. Therefore, there is a need for a reliable and economical connection between the inner components of the twist-grip shifter and the portion of the twist-grip shifter which the rider rotates to change gears.
With regard to the connection between the twist grip and the rotary part or inner twist part, one additional type of shifting mechanism which is located directly on the handlebar of the bicycle is disclosed in U.S. Pat. No. 4,938,733. This particular shifting mechanism includes front and rear handgrip shift actuators which have a cup-shaped cam member arranged generally coaxially with respect to the handlebar end portions. The cam member nests within a complementary cam cover member. After the cam member has been assembled within the cover member, a cover bushing is mounted on one end of the cover member. The cover member, being the outermost part of the above assembly, can be gripped by the rider's hand to change the gears of the bicycle transmission. The cam member, the cover member, and the bushing are connected to one another by a registration system which permits these components to rotate along with one another.